Governor



D. R. WEBB Aug. 1, I950 common Filed Dc. so, 1944 M b .b Mm F6 P mw o at nP ft E A mm 3 I H .0

Patented Aug. 1, 1950 GOVERNOR Donald B. Webb, Schenectady,

General Electric Company,

New York N. Y., assignor to a corporation of Application December 30,1944, Serial No. 570,698 Claims- (CL 170135.74)

The present invention relates to aircraft control, and more particularlyto a system for controlling the speed and pitch of the rotor of ahellcopter or other rotary wing aircraft.

Helicopters are usually provided with a powered lifting rotor or rotorshaving a plurality of blades which are hinged to the rotor hub to permitvertical movement or coning. The blades are also mounted so that theycan be rotated to adjust the pitch so that the lifting effort of therotor or rotors can be controlled. In flight, the lifting force exertedon the blade tends to pivot the blade upwardly but this upward movementis opposed by the centrifugal force of the blades which tends to keepthem in an extended position. It is very important in flight that thespeed of the rotor be kept above a minimum safe value to prevent theblades from collapsing or stalling. 0n the other hand, it is importantthat the speed of the rotor be kept below a maximum safe value to keepthe centrifugal force from stressing the rotor parts beyond designlimitations. In order to keep the rotor speed within safe limits, it isnecessary in autorotational flight to adjust the pitch of the blades andin powered flight it is necessary to coordinate both the pitch of theblades and the power output of the driving motor. This coordinationproblem, if done manually, is not only burdensome to the pilot, but mayresult in a serious crash if not performed quickly and properly.Therefore, it is desirable that means be provided for accomplishing thiscoordination automatically.

Heretofore, two different rotor speed-governing systems have beenproposed for solving this problem. In one system, referred to as athrottle governor, the throttle 0f the drive motor unit is adjusted inaccordance with the speed of the rotor to keep a constant motor androtor speed, and the lift of the rotor is then controlled by varying therotor pitch. In the other system, referred to as a pitch governor, thepitch of the rotor is adjusted in accordance with the speed of the rotorto keep approximately constant rotor speed and the lift of the rotor iscontrolled by varying the motor throttle.

The throttle governor has the advantage that the lift of the rotor isimmediately responsive to movement of the manually operated pitchcontrol so that maneuvering, especially near the ground, is facilitatedand, if necessary, the kinetic energy stored in the rotor can beutilized to provide additional momentary lift. The throttle governor hasthe disadvantage that the governing system is exceedingly diflicult tostabilize due very sluggish, making maneuvering operations An object ofthe present invention is to provide a pitch governor for controlling thespeed of a helicopter rotor which has the desirable features of both thethrottle and pitch governing systems without the above-mentioneddisadvantages.

A further object is to provide a rotor speedgoverning system which isfast acting without sacrificing stability of operation.

Another object is to provide a rotor pitch governor for a helicopterwhich responds quickly to a movement of the engine throttle to changethe rotor lift.

A still further object of the invention is to provide a helicopter rotorpitch-governing system which can be operated either manually orautomatically and which will operate automatically to reduce the pitchof the rotor if the speed of the rotor falls below a minimum safe valuewhile under either manual or automatic control.

Another object is to provide a pitch governor which is fail-safe, i. e.,one which will disconnect the governing mechanism in case of failure ofcomponent parts of the governor;

Further objects and advantages of the invention will become apparent asthe following description proceeds.

Briefly, according to the present invention, an electrically controlledservo system is provided for adjusting the pitch of the sustaining rotorblades in accordance with the speed of the rotor to maintainsubstantially constant rotor speed, the system, basically, falling intothe category of the pitch governor system referred to above. However, inorder to make the pitch of the blades immediately responsive to a changein throttle position to facilitate maneuvering, means controlled by thethrottle are provided for causing operation of the servo systemindependently of the speed of the rotor so that the pitch of the rotorblades is adjusted in a direction to anticipate a change in rotor speeddue to the changed power output of the driving motor as controlled bythe position of the throttle. In this manner,

3 transient changes in the speed of the rotor which would otherwiseoccur while the speed governing system was operating are avoided orgreatly reduced and the lift of the rotor becomes quickly responsive toa change in throttle position. This prevents a sluggish responsecondition previously found to exist in pitch governing system due to thefact that when the power of the driving motor was suddenly increased, asby opening the throttle, a considerable portion of the power wasmomentarily absorbed by the rotor in increasing the kinetic energy ofthe rotor due to the speed transient which is in a direction ofincreased R. P. M. when the power of the drive motor is increased. Inaddition, switching means are provided for rendering the pitch controlservo system inactive for manual control of the pitch of the rotor whenit is desired. However, if during manual operation the pilotinadvertently increases the pitch of the rotor to a point where therotor speed falls below a minimum safe value, means are provided forautomatically rendering the servo system active to change the pitch ofthe blade to the minimum pitch position. In

this manner, the possibility of a crash due to low rotor speed and aresulting collapsing or stalling of the blades is precluded in manual aswell as in automatic control of the rotor pitch.

For a better understanding of the present invention, reference should bemade to the following description taken in connection with theaccompanying drawings in which Fig. 1 shows a conventional helicopter towhich the present invention may be applied; Fig. 2 is a more detailedview of the rotor drive transmission showing an arrangement by which thespeed responsive tachometer and the oil pump, forming a part of theservo control system, are geared to the rotor drive shaft; and Fig. 3shows in schematic form the servo control system embodying the presentinvention.

Referring now to the drawing, there is shown in Fig. 1 a conventionalhelicopter l to which the governing system forming the subject matter ofthe present invention may be applied. It should be clearly understood,however, that my invention is not limited to this type helicopter buthas application to rotary wing aircraft generally. The helicopter isshown as being provided with a lifting or sustaining rotor comprising arotary hub 2 which is mounted on the hellcopter for rotation about anapproximately vertical axis. Radially extending from the hub 2 are aplurality of lifting blades 3 which are secured to the hub by aconventional hinging arrangement not shown. The hinging arrangementpermits the blades to flap up and down as they rotate in order tocompensate for the difference in the relative air speed of the bladeswhen they are in the advancing and receding positions during horizontalflight. The conventional hinging and mounting arrangement of the bladesalso permits the blades to be rotated about an axis extending lengthwiseof the blades so that the total pitch and lift of the blades can bevaried.

The rotor has a drive shaft 4 which is powerdriven by means of aninternal combustion engine 5 through a transmission indicated generallyat 6. As shown more clearly in Fig. 2, the transmission may comprise agear-reduction unit I, a free-wheeling clutch 8, and a bevel gear 9 fortransmitting power from the internal combustion engine 5 to a bevel orring gear 10 which is secured to the lower end of the rotor drive shaft4. The free-wheeling clutch 8 is usually pro- 4 vided in helicopters todisconnect the rotor from the driving motor in case of motor failure soas to permit a safe autorotational descent.

In the illustrated arrangement, the total pitch of the rotor blades isadjusted by means of a vertically moving shaft H which extends upwardlyto the pitch. changing mechanism (not shown) in the rotor hub 2 throughthe inside of the rotor shaft 4 which is hollow. The pitch control shaftH is coupled to a pivotally mounted pitch control lever l2 in thepilot's compartment by means of a linkage shown as comprising a bellcrank l3 and a connecting link 14. Clockwise rotation of the pitchcontrol lever l2 causes the pitch changing shaft II to move upwardly,which is in a direction to increase the pitch of the blade 3. Similarly,a counterclockwise rotation of the pitch control lever l2 causes adownward movement of the shaft II and a decrease in the pitch of theblades.

Also provided in the pilot's compartment is a throttle lever 15 whichvaries the power output of the internal combustion engine or drivingmotor 5. The connection is such that a forward or counterclockwisemovement of the throttle lever l5 acts to increase the power output ofthe driving motor 5. In some cases the throttle is in the form of amotorcycle type grip mounted on the upper end of the pitch control leverl2.

Usuall the pilot has under his control an additional cyclic pitchcontrol lever I6 by means of which horizontal flight of the helicopteris controlled. This control acts cyclically to vary the pitch of theblades as they rotate. Since the cyclic pitch control forms no part ofthe present invention, a description thereof will be omitted. It shouldbe pointed out, however, that the cyclic pitch change of the rotorblades used to control horizontal flight is different and entirelyseparate from the simultaneous pitch change of the rotor blades which isused to control the vertical lift of the rotor and the vertical flightof the helicopter. It is in connection with the simultaneous pitchcontrol that the present invention is concerned.

In the absence of an automatic pitch-governing mechanism, the pilotcontrols the vertical flight of the helicopter by a coordinated movementof the throttle lever I5 and the pitch control lever I2. Thus, forexample, if the pilot desires the helicopter to rise, he moves thethrottle lever I5 forward to increase the power output of the drivemotor 5 and at the same time moves the pitch control lever l2 backwardto increase the pitch and lift of the rotor. Similarly, if the pilotdesires the helicopter to descend, he pulls the throttle lever l5backwards and moves the pitch control lever forward to decrease thepitch and lift of the rotor. It will be appreciated that if the throttlelever and pitch control lever are not properly coordinated, the speed ofthe sustaining rotor may exceed the maximum safe value or may fall belowthe minimum safe value, in which case serious difliculty will beencountered as pointed out above.

The governing system, forming the subject matter of the presentinvention, is a means whereby the pitch of the rotor blades 3 isautomatically adjusted in accordance wit-h the speed of the rotor so asto maintain the rotor speed approximately constant at some value whichis within the safe operating range.

In order to provide means for automatically actuating the pitch changinmechanism in accordance with the speed of the rotor and the I positionof the throttle lever, there is provided a suitable servomotor ll whichmay, for example. be a hydraulic push-pull type. As shown, the hydraulicservo I1 comprises an actuating shai't l9 which is coupled to a servopiston N which moves in response to the admission of hydraulic fluidunder pressure to either end of the servo cylinder 22 through passages2| and 22 which are con-' nected to opposite ends of the cylinder. Theactuating shaft II of the servomotor is shown as being coupled to thelower end of the bell crank l2 so that as the shaft I9 moves outwardlythe pitch of the rotor blades is decreased, and as the shaft movesinwardly the pitch of the rotor blades is increased. The direction ofmovement of the servomotor i1 is controlled by means -of a control valve22 which operates to connect a hydraulic pressure line 24 to eitherpassage 2| or 22 of the hydraulic servo in accordance with the directionof vertical displacement of a three land valve element 29 from a centeror neutral position. Thus. when the valve element 2! is in the centerposition shown, the port connected to the pressure line 24 is closed andthe servomotor ll remains stationary. If, however, the valve element 25is moved upwardly, the pressure line 24 is connected to a line 29leading to the passage 2| of the hydraulic servo causing the shaft i9 tomove outwardly, the displaced oil in the servo cylinder returning to adrain line 21 through a line 29 interconnecting the valve 23 and thepassage 22. On the other hand, if the valve element 29 is displaceddownwardly from the center position, hydraulic fluid from the pressureline 24 flows through the valve 22 and the line 29 to the passage 22 andinto the opposite end of the servo cylinder, causing the shaft ii tomove inwardly, the displaced oil on the opposite side of the piston i9returning to the drain line 21 through the line 29 and the valve 22. Theporting arrangement of the valve 22 whereby the hydraulic oil isadmitted to either end of the servo cylinder 29 of the hydraulic servoI! in accordance with the displacement of the valve member 25 from itscenter or neutral position is entirely conventional and will be readilyapparent from an inspection of the drawing.

Any suitable hydraulic operating fluid, such as hydraulic oil, issupplied to the pressure line 24 by means of a suitable hydraulic pump29 which may, for example, be a gear-type displacement pump. The pump 29is driven from the rotor shaft 4 so that the servo system will continueto operate in case of engine failure. Thus the pump 29 is shown as beinggeared to the bevel gear "I on the rotor shaft 4 through a. gear traincomprising a bevel gear 29 and spur gears 2| and 92. The gears 29 and 2|may be, as shown, mounted on the shaft which drives the counter-torquepropeller located at the rear of the helicopter.

The discharge or outlet of the oil pump 29 is shown as being connectedto the pressure line 24 by a hydraulic circuit-which includes a reliefvalve or pressure regulator 92,'an oil filter 24, a manually operated"on-oil? valve 25, and a normally open, electrically operated controlvalve 39.

' The inlet or intake of the pump 29 is connected to the lower portionof a suitable reservoir or sump 21, the upper portion of which isconnected to the drain line 21 so as to complete the hydraulic fluidcircuit.

The hydraulic servo I1 is normally locked when the control valve element25 is in the center position. In order to provide means for freeing theservo piston for manual operation of the pitch control, there isprovided in the hydraulic servo a by-pass passageway 24 which normallyconnects the opposite ends of the servo cylinder. The bypass passageway29, which is normally open, is arranged to be closed by means of apiston29 which moves upwardly to the position shown against the bias of aspring 49 in response to the application of hydraulic pressure to" achamber 4| on the underside of the piston 29. The chamber 4| isconnected to the pressure line-24 by means of a line 42 so that whenthere is pressure in line 24, piston 29 is moved upwardly and theby-pass is closed, thereby conditioning the hydraulic servomotor forcontrol in accordance with displacement of the valve element 25 of thecontrol valve 22. However, upon a failure of pressure in the conduit 24,the spring 49 moves piston 29 downwardly, opening the by-pass passage 29solthat the servo piston is freed. Trapped oil on theupper side of thepiston 29 is returned to the drain line 21 through a line 42 and thecontrol valve 29.

Thus it will be apparent from the foregoing that if the oil pressurefails in line '24 due to a closing of the manually operated valve 25 ora closing of the electrically operated valve 26, the servo piston willbe freed for manual operation of the pitch controller in response tomovements of the pitch control lever I2. However, to provide againstsome emergency condition in which it would be impossible to turn oflfthe pressure supplied to line 24. there are provided additional by-passpassages 44 and 45 in the hydraulic servo which also interconnectopposite ends of the servo cylinder. The passages 44 and 45 are normallyclosed by spring-pressed ball check valves 49 and 41 which open topermit passage of hydraulic fluid between the opposite ends of the servocylinder in response to application of ab normally high hydraulicpressures. Thus in the case of an emergency, the shaft i9 of thehydraulic servo can be moved in either direction by the application ofsuflicient overpowering force to the pitch control lever |2 so that inno case is there any danger of the pitch control system being locked bythe hydraulic servomotor.

Electrically operated control valve 29 is provided for the purpose ofengaging or disengaging the hydraulic servomotor H. The construction ofthe valve may be the same as the control valve 22 previously described,and comprises a conventional three-land valve element 48 which movesvertically in either direction from a center or neutral position. Thevalve 36 is suitably ported so that when the valve member 48 is in theupper position shown, the pressure line 24 is connected to the output ofthe oil pump 29 so that the control valve 22 is supplied with oil andthe piston 39 moves upwardly to close the by-pass passage 29to renderthe hydraulic servomotor active. In this position ports are also open sothat oil trapped on the upper side of piston 39 can return to the drainline 2:! through the line 42. However, if the valve member 49 is moveddownwardly, oil pressure is cut on from the line 24 which is thenconnected to the drain line 21, and oil pressure from the pump 29 isdirected through line 43 to the upper side of piston 39 in the hydraulicservo, forcing the piston downwardly so as to open the by-pass passage38, thereby rendering the hydraulic servo inactive. Normally the valvemember 49 is maintained in the upper position shown by means of abiasing spring 49 so that the hydraulic servo and its control valve 22are conditioned for n operation. In order to move the valve element isdownwardly to disengage the hydraulic servo in response to an electricalsignal, there is provided an operating solenoid 50 which is mounted onthe upper side of the valve 35. The solenoid 50 comprises a plunger orarmature member which is' supported for vertical movement on spidersprings 52, the lower end of the plunger bearing against the top of thevalve element 43. Surrounding the armature 5| is a solenoid-operatingwinding 53 which when energized acts to pull the armature downwardly sothat the valve element 48 is moved to its lowermost position against thebias of spring 49. The manner in which the solenoid winding 53 isenergized to effect operation of the control valve 35 will be laterdescribed.

The control valve 23 which controls the direction of'movement of theservomotor I1 is operated by means of a solenoid 54, mounted on the topside of the valve which may be, as shown, of the same generalconstruction as the solenoid 50 of the control valve 36. Thus thesolenoid 54 is shown as comprisin a plunger or armature.

member 55 which is supported for vertical movement on spider springs 56,which support the armature so that the lower portion thereof bearsagainst the top of the valve element 25. rounding the plunger 55 is asolenoid-operating winding 51 which when energized acts to pull thearmature downwardly and thereby move the valve element 25 to itslowermost position against the force of a biasing spring 58 which bearsupwardly against the bottom of the valve element 25. The movement of theplunger 55 varies in accordance with theamount of current flowing in theoperating winding 51 so. that by varying the current in the operatingwinding the position of the valve element can be controlled. Thus whenthe current in the operating winding 51 has a relatively low value, thevalve element 25 moves upwardly causing the-shaft i8 of the hydraulicservo to move outwardly to decrease the pitch of the rotor blades. Onthe other hand, if the current in the operating winding of the solenoidis increased to a relatively high value, the valve element 25 moves toits lowermost position causing an inward movement of the shaft l8 of thehydraulic servo and an increase in pitch of the rotor blades. At somebalance value of current flowing in the operating winding of thesolenoid 54, the valve element 25 will remain in the center position andthe hydraulic servo will be stationary.

In order to adjust automatically the pitch of the rotor blades inaccordance with the speed of the rotor so as to maintain approximatelyconstant rotor speed, means are provided for varying the current flowingin the operating winding 51 of the solenoid 56 in accordance with therotor speed. This is accomplished by supplying cur- Surrent to theoperating winding 51 from a tachometer generator 59 which is geared tothe rotor drive shaft 4 so as to be driven at a speed proportional tothe rotor speed. Thus, as shown in Fig. 2, the tachometer generator 59has mounted on its drive shaft the spur gear 59a which meshes with spurgear 3|;which also drives the oil pump 29 as has been previouslydescribed.

The tachometer generator 59 is illustrated as being a three-phasealternating current type, the three-phase stator output windings beingindicated at 591) in Fig.2 of the drawing. Such a tachometer generatoris usually already availfrequency responsive tachometer indicator. shownat 55, which is usually mounted on the controlpanel o! the pilot'scompartment to indicate rotor speed. I

As shown in the drawing, the energizing circuit for the solenoid'winding51 ot the solenoid operating control valve 23 is electrically connectedto the three-phase output winding 55b of the tachometer generator 59 bya circuit which includes a three-phase rectifier 5|. Therefore, directcurrent is supplied to the operating winding 51 which is proportional tothe voltage output of the tachometer generator 59 which is in turnproportional to the speed oi the rotor. In this manner, the positionrotvalve element 25, and consequently the direction of movement of thehydraulic servomotor l1 and the pitch of the' rotor blades, is varied ina direction to maintain a rotor speed which corresponds to the currentin the operating'winding 51 which maintains the tive to changes incurrent flowing in the operating winding 51, an'aclditional operatingwinding 62 surrounding the armature 55 may be provided. As shown, thewinding 62 is directly connected to one of the phases of the tachometergenerator output, the connection being made ahead of the rectifier 6| sothat alternating current flows 1n the winding 62. This causes thearmature55 to oscillate so that the eflective static friction of thevalve element 23 is largely overcome, whereupon the valve is verysensitive go changes in current in the operating winding For the purposeof adjusting the rotor speed maintained by the governing system, thereis provided a rheostat 53 which is connected in series circuit relationin the energizing circuit of the solenoid winding 51. By adjustingrheostat 53. it will be apparent that the voltage output of thetachometer generator 59, and consequently the rotor speed required tocenter the control valve 23, can be adjusted as desired, The position01' rheostat 63 may be conveniently adjusted by a control knob 54 whichmay be placed, as shown, in the pilot's compartment and thereby providea simple adjustment whereby the pilot may control the governed rotorspeed.

It will be apparent that the governing system thus far described isessentially a rotor pitch governor which adjusts the pitch of the rotorblades in accordance with the speed of the rotor so as to maintainapproximately constant rotor speed.

Such a system, without further additions, is subject to theabove-mentioned disadvantage that the lift or the rotor is notimmediately responsive to a change in the position of the throttle l5 sothat maneuvering is rendered difllcult, particularly when themaneuvering is close to the ground or close to anyobject which must becleared by a precise control of the vertical position of the helicopter.Thus, for example, if the throttle i5 is suddenly opened, no controllingaction takes place until thespeed or the rotor is increased sufficientlyso that the solenoid 55 moves the valve element 25 downwardly to causethe actuating shaft l8 of the hydraulic servo to move inwardly andincrease the pitch to reduce the rotor speed. This momentary speedtransient, which is in a direction of increased R. P. M. of the rotor,results in a momentary absorption of a considerable amount of theincreased power output of the internal combustion engine 5, which poweris used in increasing the kinetic energy or the rotor. when the throttleis closed, a reverse action takes place and a speed transient occurs inthe direction or decreased R. P. M., which is required to eii'ect areduction in the Ditch oi? the blades and the kinetic energy of therotor tends to maintain the rotor lift momentarily after the throttle ismoved towards the closed position. Therefore. it will be apparent thatthe rotor llit will respond in a sluggish manner to a change in throttleposition which is undesirable ior maneuvering. In order to overcome thisdiliiculty, means are provided for causing the hydraulic servomotor iito respond immediately to a change in position of throttle I! so as tochange the pitch of the rotor blades in a direction to anticipate aspeed change or the rotor caused by a change in the power output or thedriving motor I, In the illustrated arrangement. this is. accomplishedby the provision of a rheostat 85 which is connected in series circuitrelation in. the energizing circuit or the solenoid winding 5! or thecontrol valve 23. The resistance-adjusting arm oi the rheostat 85 ismechanically coupled to the throttle lever I! so that as 'the throttleis moved in a counterclockwise or forward direction to increase thepower output of the motor I, the resistance in the solenoid-energizingcircuit is decreased. This causes the plunger 5! and the valve element25 to move downwardly whereupon the actuating shaft or the servomotor llmoves inwardly which is a direction to increase the pitch oi the rotorblades whereby transient overspeeds are prevented. Similarly, it thethrottle is moved-in a clockwise or closing direction, the rheostat itincreases the resistance of the solenoid energizingcircuit and therebydecreases thecurrent flowing therein. This causes.

the plunger 55 and the valve element 25 to move upwardly, whereupon theactuating shaft it of the servomotor moves outwardly which is in adirection to decrease the pitch of the rotor blades. whereby thetransient underspeed is prevented.

In order to limit the travel of thehydraulic servomotor and theresulting change in pitch of the rotor blades in response to a movementor the throttle lever to an amount which'is proportional to the movementoi the throttle lever, and also to prevent a change in the governingspeed which wouldotherwise be caused by the operation oi thethrottle-controlled rheostat 65, there is provided an additionalrheostat it which is also connected in series circuit relation in theenergizing circuit of the solenoid 51. The adjusting arm of the rheostat6B is connected to be operated by the actuating shalt it of thehydraulic servomotor I! in such a manner that when the shaft it movesoutwardly to decrease the rotor pitch, the resistance of rheostat 66 isdecreased and vice versa. The action is such that when the throttle IIis moved, for example, in a direction to increase the power output ofthe motorl, the resistance oi the solenoid-energizing circuit is de-.

creased, causing the servomotor shaft It to move inwardly as explainedabove, However, as the shaft I8 the servomotor moves inwardly. rheostatit operates to increase the resistance oi the energizing circuitwhereupon the solenoid plunger and the control valve element 25 arerestored to the center or balanced position, thereby stopping movementof the servomotor. If the throttle lever ii is moved in oppositedirection to decrease the power output of the driving motor I, itwill beapparent from the foregoing that the reverse action will take place.Therefore the servomotor-operated rheostat 68 sets to limit the movementof the servomotor in response to a movement of the throttle in an amountproportional to the movement of the throttle. The rheostat 66 alsooperates tomaintain approximately constant the resistance in theenergizing circuit of the solenoid 51 so that the control point a speedof the governing system is not appreciably changed by operation of thethrottle controlled rheostat .65. It should be understood that thepositioning of the hydraulic servomotor in response to the movement ofthe throttle II does not interfere with additional positioning of thehydraulic servomotor and pitch of the rotor blades in accordance withthe output or the tachometer generator 58 and the speed of the rotor.Therefore, it the speed or the rotor tends to change after the throttlesetting has been varied, the solenoid-operated control valve 23 willrespond to a change in current or the energizing circuit caused by achange in the output of the tachometer generator is to additionallyadjust the position of the servomotor and the pitch of the rotor bladesto maintain constant the rotor speed. Thus the throttle-operatedrheostat l! and the servomotor-operated rheostats it may be consideredas a follow-up system for positioning the servomotor in accordance withthe position or the throttle, this action being superimposed 7 upon thespeed-regulating action 01' the governor as controlled by the output orthe tachometer generator so.

The servomotor operated rheostat it also performs a very desirableadditional function of stabilizing the governor when it operates tochange the pitch of the rotor blades in response to a change in voltageoutput of the tachometer generator. Thus, for example, it for somereason the speed of the rotor should fall below the set value, theoutput or the tachometer generator 59 and the current flowing in thesolenoid winding I! will decrease, thereupon the valve element 28 willmove upward to cause the servomotor to move outwardly to decrease therotor pitch. This causes the rheostat 66 to decrease the resistance andtherefore increase the current in the energizing circuit or the solenoid51 so that it returns to the center or neutral position quicker thanwould otherwise be the case. This action tends to preventing hunting ofthe servomotor, whereupon more stable governor operation is obtainedparticularly when a fast acting, sensitive control valve 23 is used toobtain rapid pitch change adjustment.

As pointed out above, the solenoid-operated controlvalve 38 operateswhen energized to disable the servo system. Thereiore, when it isdesired to operate the pitch control manually, it is only necessary toprovide some switching means for connecting the solenoid winding 53 ofthe solenoid 50 to some suitable source of power. In the illustratedarrangement-the tachometer generator 59 is used tosupply the power foroperating the control valve 36 and with this arrangement an additionalprotective action is obtained as will presently be described. In orderto provide means for switching between automatic and manual operation ofthe pitch control, there is provided a switch 81 comprising a rotaryswitching member 68 which in the automatic position which the servomotoris inactive.

11 noids 6 and 52, respectively. Thus when the a switch 61 is in theposition shown in which the switching member 68 engages the contact 69,the rectified output of the tachometer generator is connected to thesolenoid 56 so that the control valve 36 is actuated according to thespeedoi the rotor for the governing action as described above. In thisposition the solenoid-operated control valve36 is deenergized so thatthe hydraulic servo is active. When it is desired to operate the pitchcontrol manually, the switching member 68 of the switch 61 is moveddownwardly so that it disengages contact 69 and engages contact wherebythe operating winding 5| of the solenoid 52 is connected to therectified output of the tachometer generator. An ad- Justable rheostatI2 is shunted across the operating winding 5| and this is adjusted sothat when the rotor speed is at the minimum safe value, the currentflowing in winding 5| is just suflicient to maintain the valve element48 of the control valve 36 in the lower position in However, if for somereason the pilot inadvertently increases the pitch of the rotor bladestoo far so that the speed of the rotor falls below the minimum safevalue, the force of biasing spring 49 0f the control valve 36 exceedsthe opposing force of the solenoid 52 and the valve element 46 movesupwardly whereupon the servomotor becomes active. It will be noted thatwhen the switching member 68 is in the lower manual position, theoperating winding 51 of the solenoid-operated control valve 23 isdisconnected, so that the valve element 25 is moved to the upperposition under the influence of the biasing spring 58. Therefore, theupward movement of the valve element 48 of the control valve 36 inresponse to a falling of the rotor speed below the minimum safe value,causes the pressure line 24 to be connected to the output of thehydraulic pump 29 and since the valve element 25 of the control valve 23is in the upper position, oil flows from pressure line 24 to line 26,whereupon the actuating shaft I8 of the servomotor l1 immediately movesto the outward position reducing the pitch of the rotor blades to theminimum value. The rotor speed will therefore increase due to thedecreased torque required to drive the rotor, but when the rotor speedincreases beyond the minimumsafe value, the valve element of the controlvalve 36 will again move downwardly, disabling the hydraulic servo andrestoring the manual control to the pilot. Thus it will be seen byenergizing the solenoid-operated control valve 36 from the output of thetachometer generator, an additional protective action is obtained whichprevents an inadvertent lowering of the rotor speed below the minimumsafe value when the pitchadiusting mechanism is under manual control.

It is believed that the operation of the helicopter rotor speedgoverning system should now be clear. Assuming that the engine 5 isrunning and that the rotor is turning, if the pilot desires that therotor speed be governed automatically, he sets the desired rotor speedby adjusting the control knob 64. He then turns the manually operatedhydraulic valve 35 to'the on position and moves the switch 66 to theupper 'or automatic position. This action deenergizesthe control valve36 and renders the hydraulic servo system operative. also connects theoperating winding of the solenoid-operating control valve 23 with theoutput 01' the tachometer generator 59.' If the speed This action 12 ofthe rotor corresponds to the setting of the speed control knob 64, thevalve element 25 of the control valve ,25 will be in the center positionand the servomotor I! will remain stationary. If for some reason thespeed of the rotor falls below the control point value, the voltageoutput of the tachometer generator 56 and the current flowing in theenergizing circuit of the solenoid system 56 will decrease, whereuponthe solenoid plunger 55 and the valve element 25 will move upwardlyunder the influence of biasing spring 56. This causes servomotor shaftl6 to move outwardly to decrease the rotor pitch, whereupon the rotorspeed increases and the valve element 25 is returned to the centerposition stopping the servomotor. Similarly, if for some reason therotor speed increases above the said control point value, the voltageoutput of the tachometer generator 56 and the current supplied to thesolenoid 55 increases, moving the solenoidplunger 55 and the valveelement 25 downwardly which causes the servomotor shaft l6 to moveinwardly to increase the pitch of the rotor blades. When the rotor speedslowsdown to the set value, valve element 25 again returns to thecenter. position due to the decreased current supplied. to the solenoidand the correcting action ceases.

If the pilot desires to increase the lift of the rotor, he opens thethrottle [5 which increases the power output of the driving motor 5 andsimultaneously decreases the resistance in the solenoid-energizingcircuit through the action of the throttle controlled rheostat 65. Thisincreases the current in the solenoid 56 so that the valve element 25moves downwardly, causing the servomotor ii to move outwardly in adirection to increase the pitch of the rotor blades thereby anticipatingand preventing an upward speed transient which would otherwise be causedby the increased power output of the driving motor 5. Conversely, if thethrottle is moved in a closing direction, the reverse action takes placeso that the servomotor l1 moves in a direction to decrease the rotorpitch, thereby anticipating and preventing a drop in rotor speed due tothe decreased output of the driving motor 5. Thus it will be seen thatthe inherent sluggish operation of the rotor speed-responsive pitchgovernor system is greatly reduced by the reduction or elimination ofrotor speed transients and the resulting change in kinetic energy of therotor as described above.

As pointed out above, the combination of the throttle controlledrheostat 65 and the servomotor eontrol rheostat 66 functions to positionthe servomotor l8 in accordance with the position of the throttle and byproperly adjusting the relationship between the rheostats, the throttlecontrolled servo movement may be selected to reduce or completelyeliminate the rotor speed transient or to over-compensate if it isdesired to use the kinetic energy of the rotor to obtain momentaryadditional lift.

As pointed out above, the servomotor controlled rheostat 66 functionsadditionally to stabilize the governing system by rebalancing thecontrol valve 25 in advance of the rotor speed returning to the setcontrol point value. In the absence of the throttle controlled rheostat65, this action would introduce a certain amount of regulation into thesystem, i. e., the governed rotor speed would vary in accordance withthe position of the servomotor. However, the action of the throttlecontrolled rheostat 651s such that the control point speed is reset tothe initial value set by the rheostat 63 whereby regulation in thecontrol point speed which would otherwise be caused by the action of theservomotor control rheostat 68 is compensated in a direction to maintainthe set rotor speed.

If the pilot desires to manually control the rotor pitch by moving thepitch control lever [2, the switch 61 is moved to the lower or manualposition thus switching the output of the tachometer generator 59 fromthe solenoid-operated servo control valve 23 to the solenoid-operatedcontrol valve 36. So long as the rotor speed is maintained above theminimum safe value, the valve element 48 of control valve 36 remains inthe lower position in which the hydraulic servomotor I! is disabled.However, if the pilot should inadvertently increase the pitch of therotor to a point where the rotor speed falls below the minimum safevalue, the valve element 48 moves to the upper position whereupon theservomotor I! is conditioned for operation as explained above. In themanual position of the control switch 61, the solenoid-operated controlvalve 23 is de-energized and the valve element 25 is in the upperposition so that the servomotor ll immediately moves the pitch controlto theminimum pitch position where it is maintained until the rotorspeed returns to a value above the minimum safe value, at which pointthe valve element 48 of the solenoid-operated control valve 35 returnsto the lower position to against disable the hydraulic servo.

If during powered flight the driving motor should fail, thefree-wheeling clutch 8 acts to disconnect the driving motor from therotor so that the rotor will continue to rotate with minimum drag. Itwill be noted that the governing system under this condition willcontinue to tunetion as before since both the tachometer generator 59and the oil pump 29 are driven from the rotor shaft 4. As the rotorstarts to slow down upon failure of the driving motor, the governingsystem will operate automatically to reduce the pitch of the rotorblades so that the rotor speed will be maintained for a safeautorotational descent.

If during flight there should for some reason occur a malfunctionin ofthe governing system, the pilot can, in an emergency, always overpowerthe governor by simply applying sufllcient force to the pitch controllever l2. Application of sufficient force to the pitch control willcause one of the by-pass valves 46 and 41 to open, depending upon thedirection of application of the force, by-passing oil between oppositeends of the servo piston so that the servo mechanism is unlocked.

It will be noted that the system is fail-safe. Thus for example if theoil pressure in line 24 should fail for some reason, the spring 40 inthe hydraulic servo moves the piston 39 downwardly so as to open theby-pass passageway 38 and thereby free the servomotor for manualcontrol. If the tachometer generator should fail when the control switch61 is in the automatic position, the control valve 23 will cause theservomotor to move the pitch control mechanism to the minimum pitchposition, thereby preventing a dangerous underspeed which might causethe blade 3 to collapse or stall. Likewise, if the tachometer generatorshould fail when the control switch 61 is in the lower or manualposition, control valve 38 will move to the uppermost position, as shownin Fig. 3, under the force of spring 49 to again cause the servomotor tomove the pitch control mechanism to the minimum pitch position.

Thus it will be apparent from the foregoing that there is provided ahelicopter rotor pitchgoverning system which, in addition to maintaininga preset rotor speed, permits the rotor lift to be quickly changed inresponse to a change in throttle position so that precise maneuvering ina vertical direction is possible, the suggish operation previouslyencountered with pitch-governing systems being prevented by theelimination of rotor speed transients. Furthermore, the system isfail-safe and in addition gives automatic pitch reduction in case ofengine failure. Also automatic rotor pitch reduction is obtained whenthe pilot is manually controlling the rotor pitch if the pilotinadvertently lowers the rotor speed below the minimum safe value.

While I have shown and described particular embodiments of my invention,it will occur to those skilled in the art that various changes andmodifications may be made without departing from my invention, and Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

l. A governing system for rotary wing aircraft having a lifting rotorand means for varying the pitch and lift of said rotor, said systemcomprising a servomotor for actuating said pitch-changing means, a firstelectroresponsive control device for controlling the direction ofmovement of said servomotor, a second electroresponsive control devicefor disabling said servomotor, a tachometer generator driven inaccordance with the speed of said rotor, and a switching device forselectively connecting said tachometer generator to said first andsecond electroresponsive control devices.

2. A governing system for a rotary wing aircraft having a lifting rotorand means for varying the pitch and lift of said rotor, said systemcomprising a servomotor for actuating said pitch-changing means, a firstdevice operable in ither direc tion from a neutral position forcontrolling the direction of movement of said servomotor in accordancewith the position of said control device, said control device havingmeans for biasing it to the direction causing said servomotor to movesaid pitch-changing means towards the minimum pitch position, andelectroresponsive actuating means for moving said control device in theopposite direction to cause said servomotor to move said pitch-changingmeans towards the maximum pitch position, a second control deviceoperable to either of two positions for rendering said servomotor activeor inactive, said second control device having means for biasing it tothe position in which said servomotor is active and electroresponsiveactuating means for moving said second control device to the otherposition in which said servomotor is inactive when the current suppliedthereto exceeds a predetermined critical value, means for producing avoltage variable in accordance with the speed of said rotor, meanscomprising a selector switch having manual and automatic positions forselectively connecting said voltage producing means to theelectroresponsive actuating means of said first and second controldevices, whereby said first control device controls said servomotor tomaintain constant speed of said rotor when said selector switch is inthe automatic position, and said second control device maintains saidservomotor inactive in the manual position unless the output of saidvoltage producing means and the current in the electroresponsiveactuating mean of said second control device falls below said criticalvalue corresponding to a minimum safe rotor speed in which case saidsecond control device moves to the position in which said servomotorbecomes active and said first device causes said servomotor to move saidpitch-changing means to the minimum pitch position.

3. A rotor speed governing system for a rotary wing aircraft having avariable pitch rotor, pitchchanging means for varying the pitch and liftof said rotor, a power means for driving said rotor, and a throtte forvarying the power output of said power means, said governing systemcomprising a servomotor for actuating said pitch-changing means, acontrol device for controlling the direction of movement of saidservomotor, means responsive to deviations in speed of said rotor from acontrol point speed for actuating said control device to cause movementof said servomotor and said rotor pitch-changing means in adirectiontocorrect for said speed deviation, means responsive to movements ofsaid throttle for causing actuation of said control device and aresulting movement of said servomotor and pitchchanging means in adirection to oppose a transient change in rotor speed which wouldotherwise occur due to the change in power output of said power means inresponse to movements of said throttle, and means responsive tomovements of said servomotor and pitch-changing means for causing theactuation of said control device and the movements of said servomotor tob limited in accordance with the amounts of movement of said throttle.

4. A rotor speed governing system for a rotary wing aircraft having avariable pitch rotor, pitchchanging means for varying the pitch and liftof said rotor, a power means for driving said rotor, and a throttle forvarying the power output of said power means, said governing systemcomprising a servomotor for actuatin said pitchchanging means, a controldevice for controlling the direction of movement of said servomotor,means responsive to deviations in speed of said rotor from a referencespeed for actuating said control device to cause movement-cf saidservomotor and said pitch-changing means in directions to correct forsaid speed deviations, means responsive to the positions of saidpitch-changing means to change said reference speed of said speedresponsive means in the direction of speed deviation to stabilize saidgoverning system, and

means responsive to the positions of said throttle to change saidreference speed'of said speed responsive means to compensate for changesof reference speed which occur due to the operation of said meansresponsive to positions of said pitch-changing mean as said throttle isadjusted to change the power output of said power means.

5. A governing system for a rotary wing aircraft having a variable pitchlifting rotor, a power plant for driving said rotor including a.throttle for controlling the power output of said power plant, saidsystem comprising a servomotor for varying the pitch and lift of saidrotor, an electric current responsive control device operable to changethe position of said servo, an electrical generator arranged to b drivenby said rotor for the generation of an electric control current of amagnitude proportional to the speed of said rotor for the actuation ofsaid control device to maintain a predetermined rotor speed byregulation of the pitch of said rotor, a follow-up control for changingthe pitch of said rotor in accordance with a change in the position ofsaid throttle comprising first and second rheostats connected in seriesbetween said generator and said current responsive control device, saidfirst rheostat being adjustable in accordance with the position of saidthrottle and said second rheostat being adjustable in accordance withthe position of said servomotor.

DONALD R. WEBB.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,374,787 Walker Apr. 12, 19211,908,894 Findley a- May 16, 1933 1,990,814 Castro Feb. 12, 19352,154,887 Baker Apr. 18, 1939 2,155,586 Ebert Apr. 25, 1939 2,187,120Gosslau et al Jan. 16, 1940 2,217,364 Halford et al Oct. 8, 19402,217,760 MacNeil et a1 Oct. 22, 1940 2,317,341 Bennett Apr. 27, 19432,325,632 Pullin Aug. 3, 1943 2,336,844 Buck Dec. 14, 1943 2,346,916Halford et al Apr. 18, 1944 2,350,126 Pitcairn May 30, 1944 2,382,847Baumann, Jr Aug. 14, 1945 2,410,659 Hoover Nov. 5, 1946 2,423,191 KoppJuly 1, 1947 Disclaimer 2,517,150.D0nald B. Webb, Schenectady, N. Y.GOVERNOR. Patent dated Aug. 1, 1950. Disclaimer filed Nov. 2, 1951, bythe assignee, General Electric Oompzmy.

Hereby enters this disclaimer to claims 3 and 4 of said patent.Ofiicz'al Gazette February 12, 952.)

